The present invention relates to the field of picture encorder, and more particularly, to the use of such picture encoders with pattern checking and classifying apparatus.
FIG. 1 is a block diagram showing the layout of a conventional pattern checking and classifying apparatus, and FIG. 2 is a timing chart which serves to explain the operation of the apparatus in FIG. 1. In FIG. 1, an object 1 on a conveyor belt 2 is examined by an imaging device 3, such as a TV camera. An illuminator 4 illuminates object 1 for examination by imaging device 3. Position sensor 5, which include a light-emitting and light-receiving device in combination, senses the position of object 1 and communicates with a timing control circuit 10.
Timing control circuit 10 is part of a video processing unit 6 which also includes an amplifier 7 connected to imaging device 3, a binary encoding circuit 8 connected to amplifier 7, and a calculating and decision-making section 9 connected to binary encoding circuit 8. The calculating and decision-making section 9 includes a video memory 91, a significant feature extracting circuit 92, an arithmetic manipulation circuit 93, a position detecting and correcting circuit 94, and a setting circuit 95.
In describing the operation of the system in FIG. 1, it is assumed that imaging device is a TV camera with three built-in shutters driven in synchronism with a vertical blanking period signal V.sub.BLK. The timing for the vertical blanking period is shown in FIG. 2(a). Position sensor 5 detects when object 1, which is transported on conveyor belt 2, reaches a predetermined position in the field of imaging device 3. FIG. 2(b) shows the output of sensor 5, which is a signal for starting the checking operation and which causes the shutter of camera 3 to open in synchronism with V.sub.BLK. That shutter opening occurs only once as shown in FIG. 2(c).
When the shutter is open, an optical image of object 1 is converted to a picture or video signal by camera 3. The video processing unit 6 then picks up an effective 1 field (1V or one half of a picture or frame) of the camera output as a video signal immediately following the opening of the shutter. The timing and duration of the image pick-up is shown in FIG. 2(d).
Amplifier 7 amplifies the input video signals and binary encoding circuit 8 converts those video signals into a binary video signal. Image memory 91 stores the binary video signal and significant feature extracting circuit 92 extracts from image memory 91 values for the various significant features of object 1. Arithmetic manipulation circuit 93 compares those significant features values with preset values obtained from setting circuit 95 and determines whether the object is acceptable or not. If the object is acceptable, circuit 93 classifies the object into an appropriate group and outputs the results on an appropriate display unit. The timing and duration of this determination and calculation operation is shown in FIG. 2(e). The position detecting and correcting circuit 94 shown in FIG. 1 detects and corrects the amount of positional offset of the object from its reference point.
The preceding discussion assumes that imaging device 3 is a TV camera with a built-in shutter. If device 3 is instead a TV camera without a shutter, a strobe or electronic flash is fired at a time corresponding to the opening of the shutter. Subsequent pattern checking and classification may then be achieved by the same procedures outlined above.
The shutter or the strobe serves to obtain a still image from a continuously moving scene, so a blurless image can be picked up to allow highly precise pattern checking and classification.
The binary encoding circuit 8 in the pattern checking and classifying system of FIG. 1 usually operates with a preset threshold value which is fixed. Such circuitry is simple, allows easy processing, and provides fast access. If, however, the brightness of illuminator 4 varies between images, or if the reflectivities of the objects under examination change from article to article, the video signals received from device 3 will vary. If these varying video signals are encoded by circuit 8 into binary signals by using a fixed threshold level, the image of the object will become heavily distorted. As a result, serious problems may occur and acceptable objects may be rejected as substandard.
A conventional method of examining an object which seeks to address this problem involves converting the video signal for one portion of the image information into a digital quantity. Density information obtained from the image information portion is then stored in a memory and subjected to information processing in order to determine an optimum level. This method, however, involves complicated circuit configurations and requires especially long processing time in order to determine threshold values.
An object of the present invention is to provide a consistent and highly precise binary encoding system which permits fast access, is economical, and is free from false responses caused by changes in illuminator brightness and object reflectivities.